The present invention provides an improvement to the read/write head actuator assembly in small disc drive systems.
In a disc drive, the read/write heads are attached to an actuator arm. A voice coil magnetic motor provides the force to move the arm about a pivot and position the heads over a desired portion of the disc. This arrangement is known as a head disc assembly.
The information supplied to the heads (write) or supplied by the heads (read) is normally carried by small wires from the heads to a point near the actuator arm pivot. A flexible printed circuit cable (PCC) is secured to the arm and the small signal carrying wires are soldered to the PCC. Additionally, the PCC carries signals to activate the moving coil motor and effectuate actuator arm rotation. In many disc drives, the PCC carries the read head signals from the moving arm to a fixed circuit board having a preamplifier to amplify the signals before sending them to a signal processing circuit elsewhere in the disc drive.
In many previous disc drive designs, the flexible PCC was bent to form an arc between the circuit board and the arm. The end was then attached to the arm, secured via an adhesive. The use of adhesive within the disc housing is usually to be avoided, except in arrangements where no other choice is apparent, because adhesives may outgas and produce particles which will contaminate the discs and or the heads. Additionally, the use of adhesives in manufacturing makes repeatable assembly very difficult and requires a cleaning step to minimize the amount of adhesive that is introduced into the disc drive environment. However disc drive designers wishing to avoid adding mass to the actuator arm have deemed a small amount of adhesive as necessary at the expense of the outgassing problems and manufacturing repeatability.
Recognizing the side effects of using adhesives in disc drives, other means for attaching the PCC to the actuator arm have been developed utilizing a screw and clamp structure as demonstrated in Jabbari et al. Ser. No. 07/611,992, U.S. Pat. No. 5,267,366, incorporated herein by reference. However, these methods required a large hole in the PCC cable to pass the screw body in order to fixably attach the PCC to the actuator arm. The resultant hole and support structure required to reinforce the receiving portion of the PCC, increased the height and mass of the PCC and therefor are less desirable in thin disc drive usage.
Another area of concern in the screw and bracket designs of the prior art is the alignment of the PCC with respect to the printed circuit board and the actuator arm assembly. When utilizing the screw and bracket attachment means of the prior art, special care had to be exercised to prevent the PCC from rotating. As the screw was tightened, rotation would often result necessitating a larger keep-out area for the PCC in the disc drive envelope or separate alignment apparatus or process steps.
In the prior art, motor sizing had to be accomplished accounting for the bias due to the arc in the PCC. Bias is the resultant force upon the actuator arm due to the arc in the PCC, thereby causing pivoting of the arm to an arbitrary position. The bias must be overcome by the actuator motor to reposition the arm. Thus, a large bias requires a powerful motor to overcome the bias. In small disc drives it is desired to design the actuator motor as small as possible. This requires using low mass parts, reducing bearing friction, and minimizing the bias.
Those ordinarily skilled in the art will recognize the larger the mass of the PCC, the larger the resultant bias. As was recited above the prior art screw and clamp mechanisms required a large hole and support structure on the PCC for use with the attachment screw, thus proportionately increasing both the mass of the PCC and the bias.
In addition to minimizing the bias, the bias must be consistent during repeated operation of the actuator arm. A consistent bias means the actuator motor can be designed and operated to overcome a specific, known bias over the full operating range of the actuator arm.
Past attempts at minimizing the bias have resulted in complex cabling strategies. One such connection disclosed in U.S. Pat. No. 4,933,785 maintains two opposing bend radii in the PCC to obtain counteracting bias forces resulting in bias minimization, a solution which is difficult to repeatably assemble.